968 Brake Pedal Travel
08-28-2014, 10:01 AM
#1
Racer
Thread Starter
968 Brake Pedal Travel
Hi all,
My first post over here, having spent most of my time in the past over on the 964 board, but I'm hoping I can tap into some wisdom on the brakes on my 968 CS.
Just wondering if anyone has come up with a workable solution to the long brake pedal travel issue ? Having done a search I have seen some reference to using a 90's BMW 7 series master cylinder, but with no detail or part number. Are there not any other bigger Porsche master cylinders that would bolt on ?
My CS is running MO30 brakes, with freshly flushed and bled Castrol SRF fluid, Pagid RS29 pads with plenty of meat, and fairly new braided hoses. I have fully plumbed brake venting with block off plates directing air right into the centre of the discs. Heat build up does not seem to be the problem - the car will stop all day long on track without fade, and the braking power is excellent, I just don't like the length of the travel and feel of the brake pedal, preferring a much firmer pedal. I have a very similar setup on my 964 RS, and whilst I appreciate the 964 braking system is a bit different, the pedal is rock-solid and stays that way regardless of abuse.
As far as I can work out, the master cylinder is the only thing that can be at fault here, and it doesn't just seem to be me that thinks this - I am aware that other 968 owners are similarly unhappy with the pedal travel. I have seen suggestions that the RHD pedal mechanism may be responsible for some "slack", but my car is LHD, so that isn't the issue for me.
Any thoughts / advice gratefully received.
thanks,
Jamie
My first post over here, having spent most of my time in the past over on the 964 board, but I'm hoping I can tap into some wisdom on the brakes on my 968 CS.
Just wondering if anyone has come up with a workable solution to the long brake pedal travel issue ? Having done a search I have seen some reference to using a 90's BMW 7 series master cylinder, but with no detail or part number. Are there not any other bigger Porsche master cylinders that would bolt on ?
My CS is running MO30 brakes, with freshly flushed and bled Castrol SRF fluid, Pagid RS29 pads with plenty of meat, and fairly new braided hoses. I have fully plumbed brake venting with block off plates directing air right into the centre of the discs. Heat build up does not seem to be the problem - the car will stop all day long on track without fade, and the braking power is excellent, I just don't like the length of the travel and feel of the brake pedal, preferring a much firmer pedal. I have a very similar setup on my 964 RS, and whilst I appreciate the 964 braking system is a bit different, the pedal is rock-solid and stays that way regardless of abuse.
As far as I can work out, the master cylinder is the only thing that can be at fault here, and it doesn't just seem to be me that thinks this - I am aware that other 968 owners are similarly unhappy with the pedal travel. I have seen suggestions that the RHD pedal mechanism may be responsible for some "slack", but my car is LHD, so that isn't the issue for me.
Any thoughts / advice gratefully received.
thanks,
Jamie
08-28-2014, 10:49 AM
#2
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Were you at Bedford Autodrome last weekend Jamie? I'm awaiting the vacation return of Ollie at RPM Technik who used to race prep 944's and was told he might have an answer. As you say, the current set up stops well but the pedal travel seems unnecessary (especially when compared to the 964's).
08-28-2014, 11:00 AM
#3
Rennlist Member
I had a similar brake travel problem with my 951 with 'Big Red' brakes. I changed all the pads and bled brakes multiple times, with no change. I did some research/investigation and found that the OEM M/C's for 944 and 951's are actually not interchangeable, but brake booster specific. This may be the same issue with your 968, since your brakes are the same as those on a 951S with ABS.
The BMW M/C that you are looking for is from a late '90s 745. When I was researching my problem I installed one in my 951 and it solved my travel problem, which help me identified the real issue with the piston travel of the stock M/C-booster combination. The BMW M/C is a better unit, but it's setup for an ABS car and since my car is non-ABS the brake line connections were more involved.
The BMW M/C that you are looking for is from a late '90s 745. When I was researching my problem I installed one in my 951 and it solved my travel problem, which help me identified the real issue with the piston travel of the stock M/C-booster combination. The BMW M/C is a better unit, but it's setup for an ABS car and since my car is non-ABS the brake line connections were more involved.
08-28-2014, 01:55 PM
#4
Racer
Thread Starter
Yes, that was me at Bedford on Saturday, though this is an issue that has been bugging me for some time. I take it you were the other 968 ???
bw993, thanks for the advice on the m/c. The 968 has ABS, so fitting may be easier - does this bolt straight up to the standard booster without any modification ?
thanks,
Jamie
bw993, thanks for the advice on the m/c. The 968 has ABS, so fitting may be easier - does this bolt straight up to the standard booster without any modification ?
thanks,
Jamie
08-28-2014, 02:55 PM
#5
Rennlist Member
It will bolt directly on a 951S, but I have never worked on a 968, so I'm not sure. You need to make sure you have a ATE brake booster to support the piston shaft length of the BMW M/C. The BMW also has the benefit of having a wider piston.
08-28-2014, 03:26 PM
#6
RL Community Team
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I think it's the wider piston that reduces the required piston travel, but I have no actual experience with it.
Might want to get a new hose for the reservoir-to-clutch MC while you're at it.
Might want to get a new hose for the reservoir-to-clutch MC while you're at it.
08-29-2014, 04:17 AM
#7
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Yup, the other 968. Seems consistent that the 968 has longer travel pedal than we're used to in the 964 (which doesn't). Obviously still does the job though and something maybe most 968 owners happily live with.
Indeed, taking Pascal's principle in hydraulics, then a wider piston diameter will apply the same pressure over shorter distance travelled (and vice versa of course). I suspect though that regular fluid changes and bleeding, new pads, performance hoses etc would go some way to 'firm up' that pedal travel. I guess alternatively jump on Demon Tweeks or other rallying/racing parts site and you can spec your own set up. Used to do a bit of historic rallying (911, MG, Lotus Sunbeam) and always in there was some AP Racing MC of spec (i.e. - http://www.rallynuts.com/motorsport-...-cylinder.html)
Indeed, taking Pascal's principle in hydraulics, then a wider piston diameter will apply the same pressure over shorter distance travelled (and vice versa of course). I suspect though that regular fluid changes and bleeding, new pads, performance hoses etc would go some way to 'firm up' that pedal travel. I guess alternatively jump on Demon Tweeks or other rallying/racing parts site and you can spec your own set up. Used to do a bit of historic rallying (911, MG, Lotus Sunbeam) and always in there was some AP Racing MC of spec (i.e. - http://www.rallynuts.com/motorsport-...-cylinder.html)